Imagine standing in front of two identical homes on the same street—same layout, same builder, same materials. You’d expect their Energy Performance Certificate (EPC) scores to be the same too, right?
Not necessarily.
Despite being physically identical, two homes can easily receive different EPC ratings. And this isn’t just a fluke—it’s surprisingly common. Let’s explore why this happens, what factors are at play, and how to avoid misleading EPC results.
🏠 1. The Role of Occupant Upgrades and Changes
Even “identical” homes may diverge the moment homeowners move in. Over time, small changes have a big impact on EPC ratings:
| Home A | Home B |
|---|---|
| Installed LED lighting | Uses older halogen bulbs |
| Upgraded boiler in 2021 | Still using original boiler |
| Added loft insulation | Loft insulation unverified |
| Sealed draughty windows | Windows slightly leaky |
🔍 Result: Home A could get a C rating, Home B a D or even E—despite identical starting points.
📋 2. Differences in Assessor Judgment & Access
EPC assessments rely heavily on visual inspections and accessible evidence. If one assessor:
Can access the loft, boiler manual, or insulation
Gets accurate documentation (like double glazing certification)
…while the other cannot, their reports will reflect that.
👤 Example: If a property owner can’t prove cavity wall insulation, the assessor must assume none exists, which can lower the EPC by a whole band.
🛠️ 3. Inconsistencies in Assessor Software or Methodology
While all EPCs in the UK use the Standard Assessment Procedure (SAP) or RdSAP, the input process can vary between assessors or software versions.
Some discrepancies may stem from:
Human error in measurements
Differences in assumptions (e.g. ventilation type)
Outdated vs. updated calculation software
📉 Even a small difference in wall thickness or window orientation can shift the final rating.
📆 4. Time of Assessment Matters
Two homes assessed a year apart may be scored using different assumptions, energy prices, or government guidelines. Energy-saving technologies (like heat pumps or solar panels) might have greater weight in newer versions of the EPC methodology.
🗓️ EPCs are valid for 10 years, but the UK government updates SAP methods more frequently than that.
💷 5. Energy Tariffs and Running Cost Estimates
EPCs also provide estimated fuel costs, and those are based on standardised fuel prices at the time of the assessment.
Home A assessed when gas prices were lower
Home B assessed during a period of high energy prices
Even if the physical structure hasn’t changed, the cost-based sections of the EPC report could differ significantly.
🧾 6. Evidence = Score
EPC assessors must “see or verify” every detail they include. If one homeowner provides:
Receipts for insulation
Manuals for efficient appliances
Proof of renewable tech
…they can boost their EPC rating, while another owner without documentation may miss out—even if they have the same setup.
📎 Tip: Keep receipts and install records for energy upgrades. Your EPC depends on it.
🛑 7. EPC Is Not a Perfect Science
Let’s be honest—EPCs are estimations, not precision energy audits. They’re designed for quick, affordable property benchmarking, not engineering-level accuracy. That means:
They don’t use actual energy bills
They assume “typical” occupancy and heating usage
They don’t account for user behaviour
So, even with the same blueprint, outcomes can vary.
✅ What You Can Do to Get a More Accurate EPC
Prepare documentation before the assessment (proof of upgrades, install dates, etc.)
Ensure full access to all areas (loft, boiler, insulation)
Use qualified, experienced assessors
Reassess if outdated — especially after improvements
🔗 Internal Linking Suggestions
📌 Conclusion: EPC Differences Are Normal—But Not Random
Two “identical” houses can have different EPCs for very real reasons—usage, upgrades, documentation, and assessor methods all matter.
Understanding these variables helps you take control of your property’s energy rating and avoid nasty surprises when selling, renting, or remortgaging.
The EPC graph is just the beginning. When you know how to read between the lines, your report becomes more than a score—it becomes a blueprint for saving energy, reducing emissions, and increasing property value.
Ready to unlock the full story of your EPC?
📅 Book your expert EPC assessment today at EPCrate.co.uk.
